During many fabricating or manufacturing processes, the piece being processed (i.e., the workpiece) shrinks. For example, a piece of porcelain typically shrinks anywhere from 12 to 16 percent during firing in a kiln. To produce a finished piece having specific dimensions, it is important to determine the exact amount the workpiece will shrink during processing and to increase the pre-processing dimensions sufficiently to allow for the determined shrinkage.
Many factors affect the exact amount of shrinkage, including the composition of the material from which the workpiece is fashioned, the size of the workpiece and the conditions under which the workpiece is processed (e.g., temperature, humidity and duration). Consequently, the amount of shrinkage can vary from the workpiece to another and from one process to another. Ideally, there should be some means to determine the exact amount a particular workpiece will shrink during a particular process.
Once the exact amount of shrinkage is determined, this amount can be factored in to the pre-processing dimensions of the workpiece. A highly convenient means to factor in this shrinkage is known in the art as a shrinkage ruler. A shrinkage ruler provides a scale that is calibrated in standard units of measure (e.g., inches or centimeters) but has a distance between successive unit designations sufficiently greater than one standard unit to allow for a specific amount of shrinkage. For example, a 10 percent scale calibrated in inches has a distance of 1-1/9 inches between successive inch designations.
Each shrinkage ruler typically provides several scales, each corresponding to a specific amount of shrinkage, such as 6, 10, 12 or 14 percent. However, unless a particular workpiece actually shrinks during a particular process by the amount specified for one of the scales, the shrinkage ruler provides only a rough approximation of the necessary pre-processing dimensions for the workpiece. For example, if the workpiece actually shrinks 71/2 percent, neither the 6 percent scale nor the 10 percent scale on the shrinkage ruler can provide accurate pre-processing dimensions. In many fabricating or manufacturing situations, such rough approximations are not acceptable.